Martínez graduated from Swarthmore College in 1946 with a degree in English. In May 2000, Swarthmore awarded Martínez with an honorary doctorate. Martínez has worked for Simon & Schuster as an editor and for The Nation Magazine as Books and Arts Editor. Her daughter, Tessa, is an actress and co-founder of San Francisco’s Latina Theater Lab.

Martínez began her political work in the early 1950s. She worked in New York for the United Nations Secretariat as a researcher on colonialism and decolonization in Africa.

During the 1960s, Martínez served full-time in the Civil Rights Movement with the Student Non-Violent Coordinating Committee in the South and as a coordinator of its New York office. In 1968, she moved to New Mexico to start a newspaper to support the Alianza Federal de Mercedes. Along with lawyer Beverly Axelrod, Martínez thus founded the bilingual movement newspaper El Grito del Norte, which she worked on for five years. In 1973, she co-founded and directed the Chicano Communications Center, a barrio-based organizing and education project.

Since moving to the Bay Area in 1976, Martínez has organized around Latino community issues, taught Women’s studies part-time, conducted anti-racist training workshops, and worked with youth groups. She ran for governor of California on the Peace & Freedom Party ticket in 1982 and has received many awards from student, community, and academic organizations, including Scholar of the Year 2000 by the National Association for Chicana and Chicano Studies. In 1997, she and Phil Hutchings co-founded the Institute for MultiRacial Justice, which "aims to strengthen the struggle against white supremacy by serving as a resource center to help build alliances among peoples of color and combat divisions." In 2004, she served on the advisory board for the group 2004 Racism Watch. She is also an adviser to the Catalyst Project, an anti-racist political education organization that focuses on white communities.